An important use of computers is the transfer of information over a network. Currently, the largest computer network in existence is the InterNet. The InterNet is a worldwide interconnection of computer networks that communicate using a common protocol. Millions of computers, from low end personal computers to high-end super computers are coupled to the InterNet.
The InterNet grew out of work funded in the 1960s by the U.S. Defense Department's Advanced Research Projects Agency. For a long time, InterNet was used by researchers in universities and national laboratories to share information. As the existence of the InterNet became more widely known, many users outside of the academic/research community (e.g., employees of large corporations) started to use InterNet to carry electronic mail.
In 1989, a new type of information system known as the World-Wide-Web ("the Web") was introduced to the InterNet. Early development of the Web took place at CERN, the European Particle Physics Laboratory. The Web is a wide-area hypermedia information retrieval system aimed to give wide access to a large universe of documents. At that time, the Web was known to and used by the academic/research community only. There was no easily available tool which allows a technically untrained person to access the Web.
In 1993, researchers at the National Center for Supercomputing Applications (NCSA) released a Web browser called "Mosiac" that implemented a graphical user interface (GUI). Mosiac's graphical user interface was simple to learn yet powerful. The Mosiac browser allows a user to retrieve documents from the World-Wide-Web using simple point-and-click commands. Because the user does not have to be technically trained and the browser is pleasant to use, it has the potential of opening up the InterNet to the masses.
The architecture of the Web follows a conventional client-server model. The terms "client" and "server" are used to refer to a computer's general role as a requester of data (the client) or provider of data (the server). Under the Web environment, Web browsers reside in clients and Web documents reside in servers. Web clients and Web servers communicate using a protocol called "HyperText Transfer Protocol" (HTTP). A browser opens a connection to a server and initiates a request for a document. The server delivers the requested document, typically in the form of a text document coded in a standard Hypertext Markup Language (HTML) format, and when the connection is closed in the above interaction, the server serves a passive role, i.e., it accepts commands from the client and cannot request the client to perform any action.
The communication model under the conventional Web environment provides a very limited level of interaction between clients and servers. In many systems, increasing the level of interaction between components in the systems often makes the systems more robust, but increasing the interaction increases the complexity of the interaction and typically slows the rate of the interaction. Thus, the conventional Web environment provides less complex, faster interactions because of the Web's level of interaction between clients and servers.
In the conventional Web environment, clients do not retain information of a session after the session is closed. In many systems, the ability to retain information after the systems become inactive is crucial to the functioning of the systems. Thus, it is desirable to allow clients to have this ability.